Active transport and absorption

Active transport and absorption

1. Active transport

   • The movement of molecules or ions in or out of a cell from an area of low concentration to high using energy or carrier molecules
   • Carrier proteins cover the plasma membranes and allow molecules or ions to transport across one side of it
     • Molecules or ions bind to receptors on the channels of carrier proteins
       • On the inside of the cell, ATP binds to the protein, producing ADP + P
         • Protein molecule changes shape and opens to the opposite side of the membrane
           • Molecules or ions are released to the other side of the membrane
             • P released from protein and recombines with ADP to form ATP during respiration
               • Protein goes back to its original shape, ready to be repeate
   • Differs from passive forms of transport by:
     • Metabolic energy (ATP) is needed
       • Materials are moved against a concentration gradient
         • Carrier protein molecules act as pumps
           • Process is selective with specific substances being transported

2. Role of diffusion in absorption

   • Glucose diffuses down a concentration gradient from inside the small intestine into the blood
     • Carbohydrates being digested in the small intestine
     • Blood is constantly circulated = glucose absorbed is constantly being removed by cells during respiration
       • Help maintain concentration gradient
   • Villi regularly contract and relax to mix contents of s. intestine
     • Help maintain concentration gradient and allows diffusion to continue

3. Role of active transport

   • Glucose absorbed from the small intestine by co-transport because of two molecules being involved
     • Glucose drawn into cells along with sodium ions that have been actively transported by the sodium-potassium pump
       • Na ions actively transported out of epithelial cells into the blood
         • Takes place in one type of protein carrier molecule
           • Higher concentration of Na ions in the lumen of the s. intestine than the epithelial cells
             • Na ions diffuse into epithelial cells down a conc. grad. through a co-transport protein in the plasma membrane
               • As Na proteins flood back through this carrier protein, they couple with the glucose molecules and are carried into the cell with them
                 • Glucose passes into blood plasma by facilitated diffusion using another type of carrier
   • Both Na ions and glucose molecules move into the cell
     • Na ions move down a conc. gad.
       • Glucose molecules move up a conc. grad
         • Na ion concentration concentration gradient that powers the movement of glucose into the cells
           • Not ATP directly
             • Indirect form of active transport